Question

What is the effciency of a rope and pulley system if a painter uses 1.93 kh of mechanical energy to pull on the rope and lift a 20 kg paunt barrel at constant speed to a height of 7.5 above the ground

Answer 1

Assuming the energy is measured in kilojoules, kJ, instead of kh:

$$\eta=\dfrac{mgh}{E}=0.76.$$